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Utilizing Beamforming Antennas for Wireless Multi-hop Networks. Romit Roy Choudhury Dept. of Computer Science University of Illinois at Urbana-Champaign. Wireless Multihop Networks. Collection of wireless hosts Relay packets on behalf of each other Together form an arbitrary topology - PowerPoint PPT Presentation
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1
Utilizing Beamforming Antennas for Wireless Multi-hop Networks
Romit Roy Choudhury
Dept. of Computer ScienceUniversity of Illinois at Urbana-Champaign
2
Wireless Multihop Networks
B
Collection of wireless hosts Relay packets on behalf of each other Together form an arbitrary topology May be connected to wired infratructure
2 reasons to prefer multihop Capacity and Power constraint
A
C
D
3
Applications
Multihop networks gained wide popularity Began with military applications
New applications proving to be commercial Already beginning to appear around us
For Example …
4
Wireless Multihop Networks
RFID
RFID
Sensors
RFID Readers
5
Wireless Multihop Networks
6
Wireless Multihop Networks
7
Wireless Multihop Networks
Internet
8
Protocol Design
Numerous challenges Connectivity (nodes can be mobile) Capacity (increasing demand) Reliability (channels fluctuate) Security QoS …
Many protocols designed
One commonality among most protocols
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Omnidirectional Antennas
Internet
10
CTS = Clear To Send
RTS = Request To Send
IEEE 802.11 with Omni Antenna
D
Y
S
M
K
RTS
CTS
X
11
IEEE 802.11 with Omni Antenna
D
Y
S
X
M
Ksilenced
silenced
silenced
silencedData
ACK
12
IEEE 802.11 with Omni Antenna
DS
X
M
Ksilenced
silenced
silenced
Y
silencedData
ACK
D
silenced
E
silencedA
silencedC
silenced
F
silenced
B
silenced
G
silenced
`` Interference management ``A crucial challenge for dense multihop networks
13
Managing Interference
Several approaches Dividing network into different channels Power control Rate Control …
Our focus Exploiting antenna capabilities
•Switched Beam Antennas•Steerable Antennas•Reconfigurable Antennas, etc.
Many becoming commercially available
For example …
14
Electronically Steerable Antenna [ATR Japan]
Higher frequency, Smaller size, Lower cost Capable of Omnidirectional mode and Directional
mode
15
Switched and Array Antennas
On poletop or vehicles Antennas bigger No power constraint
16
Antenna Abstraction
3 Possible antenna modes Omnidirectional mode Single Beam mode Multi-Beam mode
Higher Layer protocols select1. Antenna Mode2. Direction of Beam
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Antenna Beam
Energy radiated toward desired direction
A
Pictorial Model
A
Main Lobe (High gain)
Sidelobes (low gain)
18
Directional Reception
Directional reception = Spatial filtering Interference along straight line joining
interferer and receiver
A BC
D
Signal
Interference
No Collision at A
A B
C
D
Signal
Interference
Collision at A
19
Will attaching such antennas at the radio layer yield most of the benefits ?
Or
Is there need for higher layer protocol support ?
20
We design a simple baseline MAC protocol(a directional version of 802.11)
We call this protocol DMAC and investigate its behavior through simulation
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Remain omni while idle Nodes cannot predict who will trasmit to it
DMAC Example
D
Y
S
X
22
RTS
DMAC Example
D
Y
S
X
Assume S knows direction of D
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RTS
RTSCTS
DMAC Example
D
Y
S
X
DATA/ACK
X remembers not to initiate transmission toward D
24
Intuitively
Performance benefits appear obvious
25
However …
0
100
200
300
400
0 500 1000 1500 2000 2500
Sending Rate (Kbps)
Agg
rega
te T
hrou
ghpu
t (K
bps)
802.11
DMAC
Sending Rate (Kbps)
Th
rou
gh
pu
t (K
bp
s)
26
Clearly, attaching sophisticated antenna hardware is not sufficient
Simulation traces revealed various new challenges
Motivates higher layer protocol design
27
Research Contribution
Identified several new challenges
Designed MAC and Routing protocols MMAC, ToneDMAC, CaDMAC DDSR, CaRP Cross-Layer protocols – Anycasting Improved understanding of theoretical capacity
Developed prototype testbed
28
Research Contribution
Identified several new challenges
Designed MAC and Routing protocols MMAC, ToneDMAC, CaDMAC DDSR, CaRP Cross-Layer protocols – Anycasting Improved understanding of theoretical capacity
Developed prototype testbed
29
Self Interferencewith Directional MAC
New Challenges [Mobicom 02]
30
Unutilized Range [Best Paper, PWC 03]
Longer range causes interference downstream Offsets benefits
Network layer needs to utilize the long range Or, MAC protocol needs to reduce transmit power
A B CData
D
route
31
New Hidden Terminal Problemswith Directional MAC
New Challenges II …
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New Hidden Terminal Problem [IEEE TMC]
Due to gain asymmetry
Node A may not receive CTS from C i.e., A might be out of DO-range from C
B CAData
RTSCTS
33
New Hidden Terminal Problem
Due to gain asymmetry
Node A later intends to transmit to node B A cannot carrier-sense B’s transmission to C
B CAData
Carrier Sense
RTSCTS
34
New Hidden Terminal Problem
Due to gain asymmetry
Node A may initiate RTS meant for B A can interfere at C causing collision
B CADataRTS
Collision
35
Deafnesswith Directional MAC
New Challenges III …
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Deafness [ICNP 04]
Node N initiates communication to S S does not respond as S is beamformed toward
D N cannot classify cause of failure Can be collision or deafness
S D
N
Data
RTS
M
37
Channel Underutilized
Collision: N must attempt less often Deafness: N should attempt more often
Misclassification incurs penalty (similar to TCP)
S D
N
Data
RTS
M
Deafness not a problem with omnidirectional antennas
38
Deafness and “Deadlock”
Directional sensing and backoff ... Causes S to always stay beamformed to D X keeps retransmitting to S without success Similarly Z to X a “deadlock”
DATA
RTS
X
DS
Z
RTS
39
MAC-Layer CaptureThe bottleneck to spatial reuse
New Challenges IV …
40
Typically, idle nodes remain in omni mode When signal arrives, nodes get engaged in
receiving the packet Received packet passed to MAC If packet not meant for that node, it is dropped
Capture [HotNets 03]
Wastage because the receiver could accomplish useful communication
instead of receiving the unproductive packet
41
Capture Example
A B
C
D
Both B and D are omni whensignal arrives from A
A B
C
D
B and D beamform to receivearriving signal
42
Research Contribution
Identified several new challenges
Designed MAC and Routing protocols MMAC, ToneDMAC, CaDMAC DDSR, CaRP Cross-Layer protocols – Anycasting Improved understanding of theoretical capacity
Developed prototype testbed
43
Impact of Capture
Beamforming for transmission and reception only is not sufficient
Antenna control necessary during idle state also
A B
C
DA B
C
D
44
Capture-Aware MAC (CaDMAC) D monitors all incident traffic Identifies unproductive traffic
Beams that receive onlyunproductive packets are turned off
However, turning beams offcan prevent useful communication in future
MAC Layer Solution
A B
C
D
45
CaDMAC turns off beams periodically Time divided into cycles Each cycle consists of
1.Monitoring window + 2. Filtering window
1 2
CaDMAC Time Cycles
1 12 2
cycle
time
All beams remain ON,monitors unproductive beams
Node turns OFF unproductivebeams while it is idle.
Can avoid capture
46
CaDMAC Communication
Transmission / Reception uses only necessary single beam
When node becomes idle, it switches back to appropriate beam pattern Depending upon current time window
47
During Monitoring window, idle nodes are omni
Spatial Reuse in CaDMAC
A B
C
EF
D
48
At the end of Monitoring window CaDMAC identifies unproductive links
Spatial Reuse in CaDMAC
A B
C
EF
D
49
During Filtering window use spatial filtering
Spatial Reuse in CaDMAC
A B
C
EF
D
Parallel CommunicationsCaDMAC : 3 DMAC & others : ≤ 2Omni 802.11 : 1
50
Network Capacity [TechReport ‘05]
Existing results show Capacity improvement lower bounded by
Results do not consider side lobes of radiation patterns
We consider main lobe and side lobe gains (gm
and gs)
We find capacity upper bounded by
i.e., improvement of
2
O
2
1
1
21
s
m
g
g
n
W
2
s
m
g
gO
CaDMAC still below achievable capacity
51
CaDMAC cannot eliminate capture completely
Happens because CaDMAC cannot choose routes Avoiding capture-prone links A routing
problem
Discussion
YX
AB
52
Routing using Directional AntennasIncorporating capture-awareness
53
Motivating Capture-Aware Routing
YX
AB
YX
AB
D
S
Z DZ
S
Find a route from S to D, given AB exists Options are SXYD, SXZG
Capture No Capture
54
1. Sum capture costs of all beams on the route Capture cost of a Beam j =
how much unproductive traffic incident on Beam j
2. Route’s hop count3. Cost of participation
How many intermediate nodes participate in cross traffic
Measuring Route Cost
X
DS
55
Uroute = Weighted Combination of1. Capture cost (K)2. Participation cost (P)3. Hop count (H)
Weights chosen based on sensitivity analysis
Unified Routing Metric
ijipijrouteij
kroute HPU
56
CaRP Vs DSR
1
2
34
57
CaRP Vs DSR
58
CaRP Vs DSR
59
CaRP Vs DSR
60
CaRP Vs DSR
61
CaRP Vs DSR
62
CaRP Vs DSR
63
CaRP Vs DSR
64
CaRP Vs DSR
DSR CaRP
CaRP prefers a traffic-free direction“Squeezes in” more traffic in given area
65
Performance of CaDMAC
CaDMAC
DMAC
802.11
CBR Traffic (Mbps)
Ag
gre
gate
Th
rou
gh
pu
t (M
bp
s)
CMAC
66
Throughput with CaRP CaRP +CaDMAC
DSR +CaDMAC
DSR +802.11
Ag
gre
gate
Th
rou
gh
pu
t (M
bp
s)
Topology Number
Random Topologies
67
Research Contribution
Identified several new challenges
Designed MAC and Routing protocols MMAC, ToneDMAC, CaDMAC DDSR, CaRP Cross-Layer protocols – Anycasting Improved understanding of theoretical capacity
Developed prototype testbed
68
Testbed Prototype [VTC 05, Mobihoc05Poster]
Network of 6 laptops using ESPAR antennas ESPAR attached to external antenna port Beams controlled from higher layer via USB
Validated basic operations and tradeoffs Neighbor discovery
•Observed multipath
•60 degrees beamwidth useful
Basic link state routing • Improves route stability
•Higher throughput, less delay
69
Summary
Proliferation of wireless devices motivate better interference management
Most research assume omni antennas Energy radiated in all directions – inefficient
70
Omnidirectional Antennas
Internet
71
Summary
Our focus on exploiting antenna capabilities Several challenges appear Existing protocols incapable of leveraging benefits
Designed protocols at MAC and Network layer MMAC, ToneDMAC, CaDMAC Directional DSR, CaRP Analysed the upper bounds on capacity
Developed prototype testbed Capable of utilizing beamforming antennas
72
Summary
Internet
73
Other Work
Sensor Networks Reliable network-wide broadcast [submitted ICDCS]
Exploiting mobility as a carrier of gossip [StoDis 05]
K-Coverage problems
Location management in mobile networks Designed distributed algorithms [IPDPS], [Mobihoc]
Scheduling protocols for 802.11n Combination of CSMA + TDMA schemes [WTS 04]
74
Future Work
Next generation radios (software, cognitive) PHY layer not be sufficient to harness flexibility
Example•When should a radio toggle between TDMA and CSMA
?
•Dynamic channel access needs coordination
Higher layer protocols necessary for decisions
75
Future Work
Exploiting Diversity Opportunistically Especially in the context of improving
reliability
•Link diversity
•Route diversity
•Antenna diversity
•Channel diversity …
My previous work on Anycasting – a first step I intend to continue in this direction
S
A
B
C
D
76
Future Work
Sensor Networks
Strong guarantees
Weak guarantees
Solu
tion C
om
ple
xit
ySensor networks ammenableto probabilistic guarantees.
Need to design protocols that exploit this possibility
77
Future Work
Experimental Testbeds and Prototypes Evaluate protocols in real conditions Intend to build prototype testbed for sensor
and mesh networks
78
Thank You
AcknowledgmentsProf. Nitin Vaidya (advisor)
Members of my research group
CollaboratorsRam Ramanathan (BBN)
Tetsuro Ueda (ATR Labs, Japan)Steve Emeott (Motorola Labs)
Lily Yang, Guoquing Li (Intel Labs)
79
Wireless Networks
Gained popularity over last decade Cellular networks Mesh networks Wireless LANs
Several advantages Users can be mobile Low deployment cost Information access anytime-anywhere
80
Capacity Result
Wireless network capacity is shared by users
Per-user capacity upper bounded by
Implication: Relaying better than shouting
n
WO
B
A
C
D
relay relay
81
Modify
Similar to TCP on deafness – no Typo – reduscing 802.11 – say request to send Multihop in sensor MIMO – and multipath 1 slide on antenna beam/mode
Say “Antenna has 3 modes – omni, single, multi” Higher layer sets 1 mode, and direction before initiating
communication 802.11 just before DMAC 1 minute on MMAC, ToneDMAC, etc. Turning off beams has to be done before comm starts Say shortest hop first – then say DSR
82
RTS = Request To Send
RTS
CTS = Clear To Send
CTS
IEEE 802.11 with Omni Antenna
D
Y
S
X
M
K
83
Enhancing MAC [Mobicom02]
MMAC Transmit multi-hop RTS to far-away receiver Synchronize with receiver using CTS
(rendezvous) Communicate data over long links
84
Routing with Higher Range [PWC03 Best Paper]
Directional routes offer Better connectivity, fewer-hop routes
However, broadcast difficult Sweeping necessary to emulate broadcast
Evaluate tradeoffs Designed directional DSR
85
ToneDMAC’s Impact
Another possible improvement:
Backoff Counter for DMAC flows
Backoff Counter for ToneDMAC flows
time
Ba
cko
ff V
alu
es
86
2-hop flow
DMAC
IEEE 802.11
Dea
fnes
s
87
Neighbor Discovery
Non LOS and multipath important factors However, wide beamwidth (60 degrees)
reasonable envelope
Anechoic Chamber Office Corridor
88
Route Reliability
Routes discovered using sweeping – DO links Data Communication using DD links Improved SINR improves robustness against
fading
89
Optimal Carrier Sense Threshold
When sidelobe abstracted to sphere with gain Gs
T
Sidelobe Gs
Mainlobe Gd
Provided, optimal CS threshold is above the Rx sensitivity thresholdi.e., min {CS_calculate, RxSensitivity}
90
Commercial Antennas …
Paratek (DRWin scanning smart antennas) Beamforming in the RF domain (instead of digital) Multiple simultaneous beams possible, each
steerable http://www.mobileinfo.com/news_2002/issue08/Paratek_Antenna.htm
Motia Inc. (Javelin appliqué to 802.11 cards) Blind beamforming in RF domain (< 2us, within pilot)
CalAmps (DirectedAP offers digital beamforming) Uses RASTER beamforming technology http://www.calamp.com/pro_802_directedap.html
91
Commercial Antennas
Belkin (Pre-N smart antenna router – Airgo tech.) Uses 3 antenna elements for adaptive
beamforming http://www.techonline.com/community/tech_group/37714
Tantivy Communications (switching < 100 nanosec) http://www.prism.gatech.edu/~gtg139k/papers/11-03-025r0-WNG-bene
fitsofSmartAntennasin802.11Networks.pdf
92
While node pairs communicate X misses D’s CTS to S No DNAV toward D
New Hidden Terminal Problem II
D
Y
S
X
DataData
93
While node pairs communicate X misses D’s CTS to S No DNAV toward D X may later initiate RTS toward D, causing
collision
New Hidden Terminal Problem II
D
Y
S
X
Data
RTS
Collision
94
Abstract Antenna Model
N conical beams
Any combination of beams can be turned on
Capable of detecting beam-of-arrival for received packet
95
Source routing protocol (like DSR) Intermediate node X updates route cost from S -
X
Destination chooses route with least cost (Uroute) Routing protocol shown to be loop-free
Protocol Design
X
DS
C1
C2
C3
C5
USX
USD = USX + C2 + C5 + PD + 1